FIG. 1 shows a conventional vertical probing unit 1, which must include a spring mechanism 2 in order to perform elastic compression characteristics and to provide cushioning when a probe 3, which is connecting to one end of the spring mechanism 2, contacts to a pad 9 of a device under test (hereinafter referring to as “DUT”). In such a manner, a better contact performance between the probe 3 and the pad 9 can be achieved while preventing the probe 3 or the DUT from being damaged caused by an excessive contacting pressure.
FIG. 2 shows another conventional vertical probing unit 5 having a similar spring mechanism, but differing from the above-mentioned spring mechanism by including a first spring 6 and a second spring 7. An outer end of the first spring 6 is connecting to a probe 6a, and an outer end of the second spring 7 is connecting to a shaft 7a. In other words, the probe 6a and the shaft 7a of the vertical probing unit 5 are position changeable upon pressed, in order to be adapted for different usage environments. Such vertical probing unit can achieve the same performances as the above-mentioned probing unit 1.
Although the conventional probing units can fulfill the objective of the functional testing, there are still some drawbacks, especially when it comes to the transmission of HF signals, remained to be overcome. Generally speaking, a probing unit having good HF signal transmission performance enhances the precision and quality of DUT testing. However, those conventional probing units have the same or similar characteristic in that the spring mechanisms thereof are confined in a barrel having inner walls. As shown in FIG. 1, the spring mechanism 2 is located between two parallel side walls of a protective rod 4, while the first spring 6 and the second spring 7, as shown in FIG. 2, are located in the barrel 8. Thereby, the width W of the spring mechanisms is confined. This becomes disadvantageous since the performance of the probing unit is significantly affected when the size thereof becomes smaller and smaller. This is so because the protective rod 4 or the barrel 8 occupies relatively a small amount of space within a limited aperture of a jig. Moreover, the conventional elastic probe is movable only in the vertical direction. Such design is not suitable for use when requiring to laterally scrape the surface oxide layer off a planar pad of the DUT, and thus the contact resistance may become too large to undergo such type of testing procedures.
Therefore, our expectation is to enlarge the width of the spring mechanism to the maximum value under the constraining requirements of the limiting outer diameter D, i.e. the outer diameter of the protective rod or the barrel, and the restriction of the yield strength of the material, so as to achieve the best compression performance, i.e. the best working stroke, while shortening the total length of the spring mechanism. In such a manner, the inductance of the signal transmission can be lowered, so as to increase the bandwidth. Furthermore, it is desirable to control the movement of the spring through changes in structural design to meet the requirements of different DUTs. For example, if the tip of the probe can be configured to laterally scrape the surface oxide layer off the planar pad during testing, the contact resistance thereof can be more stable to achieve a better testing quality compared with the conventional elastic probe contacting the planar pad in a vertical-movement-only manner.